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THG's Hurricane Florence WMHB (2018)
Hurricane Florence '''was an unusual, deadly tropical cyclone and was the third-costliest tropical cyclone of the 2018 Atlantic Hurricane Season, as well as the 4th-wettest tropical cyclone on record, dumping over 50 inches of rain in parts of the northeast. Hurricane Florence was the 6th named storm, 4th hurricane, and the 2nd major hurricane of the 2018 Atlantic Hurricane Season. Florence originated from a strong easterly tropical wave, south of the Cape Verde Islands on September 16, 2018. The nascent tropical disturbance steadily organized, until the MCHWS designated it as "Florence", on September 17th. On a progressive westward trajectory, Florence acquired tropical storm strength, with max sustained winds at 45 MPH on the Saffir-Simpson scale, by Dvorak and scatterometer estimates. On September 19th, Florence strengthened to a category 1 hurricane, with max sustained winds at 74-95 MPH (119-153 Km/h), heading west-northwest at 13 MPH. Florence turned northwest after a decrease in forward speed. Florence started to gain stronger convection overnight on September 20th, strengthening to a category 2 hurricane. A high pressure to the north aiding in a decrease in forward speed favored further intensification, early on September 21, and Florence turned west. Weather models consistently showed a threat somewhere from the Mid-Atlantic to the northeast, so early preparations were in place all along the eastern seaboard. The MCHWS issued tropical storm watches ahead of now category 4 hurricane Florence in Bermuda for potential impacts. On September 22nd, Hurricane Florence reached peak intensity as a minimal category 5 hurricane, but only for 6 hours, as below normal water temperatures hindered further strengthening. Florence slowly weakened to a category 3 hurricane. On September 24th, it was becoming increasingly likely that Florence will be a high impact storm all along the northeast coast. On September 25th, Florence turned extratropical and landfalled with max sustained winds of 80 MPH, and stalled, bringing devastating flooding in New York and Long Island. Up to 50 inches of rain caused flooding and storm surge which killed 29 people. Florence gained forward speed on the 27th and hauled northeast, eventually dissipating before reaching Iceland. '''Meteorological History On September 14, a broad area of low pressure associated with a tropical wave moved off the coast of Africa. The MCHWS invested the disturbance, at 5 PM AST, September 14. Initially, the MCHWS gave the disturbance a 50 percent chance of development, due to slightly unfavorable upper-level wind shear and below normal water temperatures. Meteorologists began using the Dvorak technique, and on September 15, satellite observations showed a well-defined low level circulation but somewhat disorganized convection due to moderate southwesterly wind shear. Based on a T-number of 3.5, the MCHWS assigned the disturbance "Florence", defining Florence with 65 MPH winds and a minimum pressure of 997 mbar. Under the influence of a high pressure retrograding to the east, Florence slowly started to gain more latitude. On September 17, Florence was marked with an increase in forward speed, due to the presence of the strengthening high pressure to the north. A well defined CDO with slight indications of a central eye prompted Florence to reach hurricane status, during the evening of the 17th. On September 18th, wind shear unexpectedly lowered to around 10 kt, which allowed Florence's increasing intensity to accelerate. Florence rapidly developed a clear eye. Florence became a major hurricane, with winds of 120 MPH, at 0500 UTC, on September 19th. Hurricane hunters were scheduled to fly into Florence and departed Puerto Rico at 1200 UTC, September 19th, and found a tight circulation with flight level winds exceeding 125 MPH. However, a series of dropsondes in the northwest and northeast eyewall concluded that the intensity had leveled off, possibly due to cloud tops which had slightly warmed since the period of intensification began a day earlier. At 0300 UTC, September 20th, a high pressure node forced Florence to move west. A trough was diving down from the Canadian Maritimes, but did not amplify enough to provide a clear escape route to the northeast. Florence become an anomalous cyclone, as no hurricanes within 100 miles of Florence took a westward turn and directly impacted land in history. Late on September 20th, an upper-level dropsonde mission was conducted, and dropsonde data was ingested into the global weather models. Florence was entering a more favorable environment and dry air was starting to moisten up, however an Eyewall Replacement Cycle prevented Florence from rapidly intensifying until a little later. On September 21st, Florence began to re-intensify after a 12-hour intensity fluctuation, and the MCHWS correctly predicted category 5 intensity, and Florence became a category 5 hurricane with max sustained winds of 160 MPH (257 Km/h), and a minimum central pressure of 928 mbar. That intensity was shortlived, however, water temperatures at the time were below normal, as much as 0.5-2C. This prompted Florence to weaken from peak intensity. Hurricane Florence began to slowly weaken, and it was evident that a re-intensification was unlikely at that latitude. On September 22nd, computer models continuously depicted a possible weak hurricane/ strong tropical storm landfalling somewhere in New England. This put northeast residents on high alert, and the New York governor declared a state of emergency, Connecticut soon to follow, and preparations for a potential landfall begun. Florence weakened further to category 3 intensity, and forward speed increased. Upper level stream flows directed Florence northwestward, on a trajectory to possibly Long Island or Cape Cod, Massachusetts. At 11 AM EST September 23rd, the MCHWS issued hurricane watches and tropical storm watches from the outer banks of North Carolina, to Maine. On September 24th, all watches were upgraded to warnings, as Florence was less than 24 hours away from landfall. Computer models suddenly started to depict a stall scenario over New York, as current observations at the time supported the model runs. An enormous dead high pressure cell extended from the western United States to the North Atlantic Ocean, and Florence began to slow down. Then, hurricane Florence made landfall on the 25th, at 1:25 AM EST, after turning extratropical with max sustained winds of 75 MPH, shortly before being downgraded to a tropical storm. Wind gusts of up to 100 MPH were reported at various stations in Long Island, and lesser wind gusts of 60-80 MPH inland. Florence's slow movement of 2-4 MPH went on for nearly a day while dropping very heavy rain, and was caused by collapse of strong steering currents. A storm surge of 10 feet was reported in Montauk. On September 26th, Florence was picked up by a strong, northerly jet stream trough from the Canadian Provinces, and Florence's forward speed increased markedly to 25 MPH, and weakened to a remnant low over Nova Scotia on the 27th. Florence transitioned to a frontal system and dissipated a few hundred miles west of Iceland. MCHWS issued its final advisories at 8 PM, September 28th. Impacts Bermuda Hurricane Florence's impacts on Bermuda were relatively minimal, due to the proximity being too far for any direct impacts. There were rip currents, which killed one person. North Carolina During Florence's passage a few hundred miles east, a rip current caused a man to drown. Florence produced up to 0.5 inches of rain in the outer bands, mainly inland. Higher impacts were mainly confined to the immediate coastline of the Outer Banks. Wind gusts possibly reached 30 MPH, along with 15 foot waves. Category:Category 5 Atlantic hurricanes Category:Deadly storms Category:Costly storms